Many different types of gas sensor housings or units have been implemented in environments containing corrosive gases. In this type of situation, the gas sensor housing can be operatively connected to a central station to form a gas sensing signaling system or device. In the context of automotive exhaust gas applications, in order to reduce the automotive emission levels it is of prime importance to measure the constituents of exhaust gas (e.g., NOx, So2, CO, CO2, etc). In industrial applications, the ability to monitor and detect gas is also of primary importance.
In order to protect industrial plants or installations, pipe conduit channels, chemical storage areas and so forth, against fires and also to prevent humans from being exposed to toxic gases, it is desirable to detect at an incipient stage, dangerous concentrations of combustible or noxious gases. In response to such detection, it is then possible to initiate suitable counter measures, for instance shutting down operating installations, which are improperly functioning, closing off leaking pipe conduits, starting ventilators or other exhaust apparatus, opening emergency exits and otherwise signaling the occupants or personnel of the need to leave the area. In this manner fires, explosions, toxic effects and other damage may be prevented. Thus, In order to detect undesired and dangerous concentrations of oxidizable or combustible gases, gas sensing signaling or alarm systems composed of gas sensing units can be implemented, which are connected with a central station.
A typical gas sensing unit contains a gas sensor which, when exposed to the action of reducible gases, alters its electrical resistance. In terms of physical construction, electrochemical gas sensors usually include some type of external housing, which acts as a reservoir for an electrolyte. A wick may be utilized to keep the electrolyte in contact with the electrodes. External electrical terminals are also often provided, which make electrical contact with the electrodes. Many commercially available gas sensors are of the amperometric type having two or more electrodes in which a catalytically active metal is fixed to a porous substrate.
In one prior art gas sensor design, a planar sensing element can be immobilized in gas-tight fashion, by way of a sealing element, and implemented in a pass-through component of an exhaust-gas-side lower ceramic shaped element. The exhaust-gas-side ceramic shaped element can possess, on the end surface and facing away from the exhaust gas, a recess that surrounds the pass-through and into which a glass seal is introduced. A further ceramic shaped element is then joined via a metal solder join to the housing on the glass seal. The glass seal encloses the sensing element inside the recess, and constitutes a gas-tight join between ceramic shaped element and sensing element at this point. One of the problems with this type of gas sensor configurations is that the effect of high temperatures causes errors in the functionality of the sensor system.
Another type of gas sensor configuration includes the use of a sensor element that is fixed in a tubular, metallic housing in a gas-tight manner. At its lower part, the tubular housing contains a lip facing radially outward and which forms a sealing flange. Such a gas sensor can be mounted in an opening of an exhaust system, with the lip sitting on a sealing seat formed in the opening. A banjo bolt can be led over the housing and screwed into a thread arranged in the opening, thereby joining the lip to the exhaust system in a gas-tight manner. Problematic in this design is, however, that the pressing or upsetting of the relatively thin-walled material of the housing can produce micro-cracks at the lip, which can cause the housing to leak.
O2 (oxygen), NOx (nitrogen oxide), NH3 (ammonia), SOx (sulphur oxide), CO (carbon monoxide) and CO2 (carbon dioxide) sensors are used in automotive exhaust gas pipes in most gasoline and diesel engines to control pollution and improve combustion performance. Exhaust gas contains soot particles and unburned carbon, which can damage the sensors and erode the sensor element. The sensing element of such sensors can be exposed to a very high temperature of the exhaust gas (excess of 500 C). The sensing element utilized in such sensors may also be directly exposed to high flow velocity of the exhaust gas . . . Prior art sensors, however, do not achieve such parameters.
Prior art sensors are subject over a period of time to errors that can increase due to drift, etc. Additionally, at the temperatures described above, such sensors degrade rapidly. Based on the foregoing, it can be appreciated that designing gas sensors to function at these temperatures is a precise and costly endeavor. Hence to overcome the effect of soot and high temperature, an innovative packaging concept is proposed as described in greater detail herein.